The invention relates generally to lock nuts threadably engageable and lockingly retainable about a threaded shaft, and more particularly to lock nuts which are undeformed prior to installation, and lock nuts having improved torque performance, while providing extremely low "first on" torques, including relatively consistent torque performance with reduced statistical spread over several installation and removal cycles.
Lock nuts have many configurations and are used widely in industry.
U.S. Pat. No. 2,142,819 entitled "Self Gripping Device" issued on Jan. 3, 1939 to Olson and commonly assigned herewith, for example, discloses a locking nut having diametrically opposed slots disposed transversely therein to form yieldable sections, which are deflected axially to distort a portion of the threaded bore by helical disalignment thereof along the yieldable sections, prior to installation thereof, thereby providing a balanced frictional grip on a threaded shaft subsequently disposed through the threaded bore of the lock nut.
U.S. Pat. No.3,659,491 entitled "Rotatable Nut and Washer Assembly" issued on May 2, 1972 to Duffy et al. discloses a lock nut formed of a threaded inner barrel coupled by a web to a hexagonally shaped outer barrel having a radially extending peripheral skirt, which is formed as a unitary nut member. The nut of U.S. Pat. No. 3,659,491 is rotatably coupled to a frusto-conical spring washer, which forms an assembly, wherein the spring washer is flattenable between the nut and a workpiece, to provide a reverse axial tension on the nut and a radially inwardly directed compressive force on the inner barrel, which locks the nut about a threaded shaft. The spring washer in U.S. Pat. No. 3,659,491 becomes rotationally fixed relative to the workpiece, thereby reducing the torque required to install the lock nut about the shaft and thereby also reducing damage to the surface of the workpiece, which otherwise occurs when the washer is rotationally fixed relative to the nut. The lock nut of U.S. Pat. No. 3,659,491 however is relatively expensive to manufacture, particularly the unitary nut portion, which is fabricated from sheet metal.
Generally, prior art lock nut retention performance is diminished substantially upon removal of the nut from the threaded shaft. In lock nuts of the type disclosed in U.S. Pat. No. 2,142,819 discussed above, the diminished retention performance results from a tendency of the slots to widen after the lock nut is disposed about the shaft during the first installation and subsequent first removal therefrom. This adverse effect on prior art lock nut retention performance is particularly significant after the first installation and removal cycle, and continues to worsen as the lock nut is subject to repeated cycles of installation and removal, which commonly occurs in applications where the nut must be removed and reinstalled for service and maintenance.
FIG. 9 of the present patent application illustrates graphically the torque performance of prior lock nuts over several installation and removal cycles generally, and more particularly illustrates the relatively large torque required for the first installation, or first on, in comparison to the substantially reduced torque required for the first removal, or first off, wherein the torque performance continues to diminish, though at a lesser rate, with increasing numbers of on and off cycles. FIG. 9 also illustrates the relatively inconsistent torque performance of prior art lock nuts, particularly over the interval between the "1 ON" through the "3 OFF" whereafter the torque performance is more consistent over the interval between the "3 OFF" and the "5 OFF". FIG. 9 illustrates further the tendency of prior art lock nut torque performance not to comply with an industry established torque specification as it decreases below the SPEC curve somewhere between the "2 OFF" and "3 OFF", which often results from the relatively large statistical spread associated with the torque performance of prior art lock nuts.
The copending U.S. application Ser. No. 08/628,923 entitled "Prevailing Torque Nut" discloses a novel lock nut configuration having relatively consistent torque performance and reduced statistical spread over several repeated cycles of nut installation and nut removal about a threaded shaft, which is a remarkable improvement over prior art lock nuts. The copending U.S. application Ser. No. 08/628,982 entitled "Method for Sizing a Lock Nut" discloses a method of manufacturing a lock nut that includes a step of threading an enlarged sizing tool through a deformed portion of a lock nut threaded bore during the manufacture thereof and prior to actual use of the lock nut, which further improves the torque performance thereof. More particularly, the sized lock nut of U.S. application Ser. No. 08/628,923 has among other advantages a relatively more consistent torque performance over several installation and removal cycles, including a reduced first on torque and reduced statistical spread. The threaded bore portions of these lock nuts however are deformed prior to installation.
The present invention is drawn to improved lock nuts that overcome problems in the prior art, and more particularly to lock nuts having further improvements in torque performance, including greater consistency of torque performance, substantially reduced first on torque, and reduced statistical spread.
It is a more particular object of the present invention to provide a novel lock nut threadably engageable and lockingly retainable about a threaded shaft extending through a workpiece, the lock nut having at least one deformable slot disposed on a side portion thereof and disposed transversely relative to the lock nut bore axis, the lock nut also having a nut deforming member protruding from a bottom end thereof, wherein at least a portion of the nut deforming member is in substantial axial alignment with the deformable slot. Notably, the lock nut is undeformed prior to installation thereof about the threaded shaft. The nut deforming member is however engageable with the workpiece to deform the lock nut upon threadably installing the lock nut about the threaded shaft, thereby retaining the lock nut thereabout, whereby the lock nut has a relatively consistent torque performance with reduced statistical spread over several installation and removal cycles of the nut about the threaded shaft.
It is also an object of the invention to provide a novel lock nut of the more particular configuration described above, wherein the lower portion of the lock nut includes a skirt extending outwardly beyond the side portion thereof, and wherein the nut deforming member is an annular portion of the skirt disposed peripherally on the lower end thereof, wherein a bottom portion of the lock nut has a substantially concaved or countersunk surface.
It is another object of the invention to provide a novel lock nut of the more particular configurations described above, wherein the lock nut includes a plurality of at least two deformable slots disposed on side portions thereof and a corresponding plurality of nut deforming members disposed on the bottom end of the body member in substantial axial alignment with the corresponding deformable slot. In one embodiment, the deformable slots are disposed substantially transversely to the bore axis and substantially symmetrically thereabout, and in another embodiment one or more of the plurality of deformable slots is offset axially along the bore axis relative to the other deformable slots.
It is a further object of the invention to provide a novel lock nut of the more particular configurations described above, wherein the lock nut includes a substantially conical spring washer rotatably coupled to the lower portion of the body member. A sloping upper surface of the spring washer slopes away from the bottom end of the body member and accommodates the one or more nut deforming members therebetween, whereby the nut deforming members are engageable with the upper surface of the spring washer to deform the body member upon clamping and flattening the spring washer between the bottom end of the body member and a workpiece.
These and other objects, features and advantages of the present invention will become more fully apparent upon careful consideration of the following Detailed Description of the Invention and the accompanying Drawings, which may be disproportionate for ease of understanding, wherein like structure and steps are referenced by corresponding numerals and indicators.